1. Field of the Invention
The present invention relates to a fluid flow regulation system and in particular to a fluid flow regulation system for regulating a gas flow, especially of an additive gas, in a patient breathing circuit of a mechanical breathing aid.
2. Description of the Prior Art
A known fluid flow regulation system has a valve arrangement with an inlet flow path which terminates in a valve opening, an outlet flow path in fluid connection with the valve opening and a sealing element which co-operates with the valve opening to provide an adjustable regulation of flow through the valve arrangement. The sealing element is movable to a closed position in which it presses against the valve opening to seal it against fluid through-flow and to an open position in which it is displaced from the valve opening to establish a desired through-flow which is adjustable by varying the amount of displacement relative to the valve opening. It is also known to employ such a system to regulate the delivery of small amounts of an additive gas into a breathing gas for supply to a patient. In this arrangement the inlet flow path is connected to a supply of the additive gas and the outlet flow path is connected to an inspiration side of a patient breathing circuit which is intended to provide a gas flow path between a mechanical breathing aid, such as a ventilator, respirator or anaesthetic device, and a patient's airways.
A problem with this known regulation system concerns the sealing element of the valve arrangement. If the part of the element which seals against the valve opening is formed of a rigid material, then small desired flows may be accurately established but a proper sealing in the closed position is difficult to achieve and a leakage flow prevails even in the closed position. However, if a less rigid, resiliently deformable, material is used for that part of the sealing element, a fluid tight seal can be established in the closed position since the element can more readily be deformed to the shape of the valve opening, but small flows can be less accurately established because of a hysteretic effect in the displacement of the sealing element caused by the sealing element having to regain its original shape before it moves away from the valve opening.